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diff --git a/browser/components/resistfingerprinting/test/mochitest/file_animation_api.html b/browser/components/resistfingerprinting/test/mochitest/file_animation_api.html
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index 0000000000..376fddf343
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+++ b/browser/components/resistfingerprinting/test/mochitest/file_animation_api.html
@@ -0,0 +1,104 @@
+<!DOCTYPE HTML>
+<html>
+<head>
+  <meta charset="utf-8">
+  <title>Test for Bug 1382545</title>
+<script>
+  function waitForCondition(aCond, aCallback, aErrorMsg) {
+    var tries = 0;
+    var interval = setInterval(() => {
+      if (tries >= 30) {
+        opener.ok(false, aErrorMsg);
+        moveOn();
+        return;
+      }
+      var conditionPassed;
+      try {
+        conditionPassed = aCond();
+      } catch (e) {
+        opener.ok(false, `${e}\n${e.stack}`);
+        conditionPassed = false;
+      }
+      if (conditionPassed) {
+        moveOn();
+      }
+      tries++;
+    }, 100);
+    var moveOn = () => { clearInterval(interval); aCallback(); };
+  }
+
+  function runTest() {
+    let expectedPrecision = opener.expectedPrecision / 1000;
+    let isRounded = (x) => {
+      let rounded = (Math.floor(x / expectedPrecision) * expectedPrecision);
+      // First we do the perfectly normal check that should work just fine
+      if (rounded === x || x === 0)
+        return true;
+
+      // When we're diving by non-whole numbers, we may not get perfect
+      // multiplication/division because of floating points.
+      // When dealing with ms since epoch, a double's precision is on the order
+      // of 1/5 of a microsecond, so we use a value a little higher than that as
+      // our epsilon.
+      // To be clear, this error is introduced in our re-calculation of 'rounded'
+      // above in JavaScript.
+      if (Math.abs(rounded - x + expectedPrecision) < .0005) {
+        return true;
+      } else if (Math.abs(rounded - x) < .0005) {
+        return true;
+      }
+
+      // Then we handle the case where you're sub-millisecond and the timer is not
+      // We check that the timer is not sub-millisecond by assuming it is not if it
+      // returns an even number of milliseconds
+      if (expectedPrecision < 1 && Math.round(x) == x) {
+        if (Math.round(rounded) == x) {
+          return true;
+        }
+      }
+
+      // We are temporarily disabling this extra debugging failure because we expect to return false in some instances
+      // When we correct things we will re-enable it for debugging assistance
+      // opener.ok(false, "Looming Test Failure, Additional Debugging Info: Expected Precision: " + expectedPrecision + " Measured Value: " + x +
+      //   " Rounded Vaue: " + rounded + " Fuzzy1: " + Math.abs(rounded - x + expectedPrecision) +
+      //   " Fuzzy 2: " + Math.abs(rounded - x));
+
+      return false;
+    };
+    const testDiv = document.getElementById("testDiv");
+    const animation = testDiv.animate({ opacity: [0, 1] }, 100000);
+    animation.play();
+
+    waitForCondition(
+      () => animation.currentTime > 100,
+        () => {
+          // We have disabled Time Precision Reduction for CSS Animations, so we expect those tests to fail.
+          // If we are testing that preference, we accept either rounded or not rounded values as A-OK.
+          var maybeAcceptEverything = function(value) {
+            if (opener.prefName.includes("privacy.reduceTimerPrecision") &&
+                !opener.prefName.includes("privacy.resistFingerprinting"))
+              return true;
+            return value;
+          };
+
+          opener.ok(maybeAcceptEverything(isRounded(animation.startTime)),
+             "pref: " + opener.prefName + " - animation.startTime with precision " + expectedPrecision + " is not rounded: " + animation.startTime);
+          opener.ok(maybeAcceptEverything(isRounded(animation.currentTime)),
+             "pref: " + opener.prefName + " - animation.currentTime with precision " + expectedPrecision + " is not rounded: " + animation.currentTime);
+          opener.ok(maybeAcceptEverything(isRounded(animation.timeline.currentTime)),
+             "pref: " + opener.prefName + " - animation.timeline.currentTime with precision " + expectedPrecision + " is not rounded: " + animation.timeline.currentTime);
+          if (document.timeline) {
+            opener.ok(maybeAcceptEverything(isRounded(document.timeline.currentTime)),
+               "pref: " + opener.prefName + " - document.timeline.currentTime with precision " + expectedPrecision + " is not rounded: " + document.timeline.currentTime);
+          }
+          opener.done();
+          window.close();
+        },
+        "animation failed to start");
+  }
+</script>
+</head>
+<body onload="runTest();">
+<div id="testDiv">test</div>
+</body>
+</html>